Plot3D[x/Exp[x^2+y^2],{x,-2,2},{y,-2,2}]
Plot3D[Tan[x+y],{x,-3,3},{y,-2,2}]
Plot3D[Cot[x+y],{x,0,5},{y,0,3}]
Plot3D[x^2+y^2,{x,-2,2},{y,-2,2}]
Plot3D[x^4-2*x^2+y^4-2*y^2+5,{x,-2,2},{y,-2,2}]
Plot3D[(x^2+y^2)*Exp[1-x^2-y^2],{x,-3,3},{y,-3,3}]
